1. Field of the Invention
The present invention relates to a method and an apparatus for effecting treatment on a surface of an object, i.e., a work and more particularly for effecting treatment such as film deposition, etching or quality modification by exposing a work to be treated to a plasma and implanting ions in the plasma into the work.
2. Description of the Background Art
PSII (Plasma Source Ion Implantation) has been known as a technology for surface treatment of an object, and an example of an apparatus for the same is shown in FIG. 6.
This apparatus has a grounded vacuum container 1. An exhaust device 11 and a treatment gas supply unit 3 are provided for the container 1. The treatment gas supply unit 3 includes a mass-flow controller, a gas source and others, which are not shown in the figure. An electrode 2 also serving as a holder for supporting a work S, i.e., an object to be treated is arranged in the container 1. The electrode 2 is connected to a DC high-voltage source 22 through an on-off switch 21. A filament 4 which is supplied with an electric power and thereby is heated for emitting electrons is arranged in the container 1. The filament 4 is connected to a filament power source 41 and a discharge bias power source 42.
For effecting surface treatment on the work S by this apparatus, the work S is transported into the vacuum container 1 by an unillustrated work transporting device, and is held by the holder 2. Then, a treatment gas such as nitrogen gas is supplied into the container 1 from the gas supply unit 3 while keeping a predetermined degree of vacuum in the container 1 at the order of 10.sup.-4 by operating the exhaust device 11. Also, the filament power source 41 energizes and thereby heats the filament 4 to emit electrons, and the discharge bias power source 42 applies a bias voltage to the filament 4 to accelerate the emitted electrons. Thereby, the treatment gas which is introduced as described above is ionized to form plasma P. During this, the electrode 2 is supplied with a negative high-voltage pulse from the power source 22 through the on-off switch 21. Thereby, the surface of the work S is exposed to the plasma P, and the positive ions in the plasma P are accelerated toward the work S and are implanted into the surface of the work S so that treatment such as modification of quality is effected on the surface of the work S.
According to the above apparatus and method for the surface treatment, predetermined treatment can be effected relatively uniformly on the surface of the work having a complicated three-dimensional structure.
However, the apparatus and method for the surface treatment in the prior art suffer from the following problems. For example, a work, such as an object used in semiconductor device, may have different kinds of portions, i.e., a portion which is covered with an electrically insulating material or is in a floated potential, and a portion which is made of an electrically conductive material, such as an electrically conductive circuit, and it may be desired to effect the treatment only on the above conductive portion. In the processing for this treatment, a pulse voltage is not applied to the insulated portion or the portion carrying the floated potential (both of which will be generally termed as the "insulated portion"), and the positive ions are not ideally implanted into the insulated portion. However, due to the weight of ions, the ions cannot rapidly change their course at the vicinity of the surface of the insulated portion during an on-period of the pulse voltage so that the ions collide with and are implanted into the surface of the insulated portion at and around its end. Generally, when ions are implanted into a work surface with a high energy from about several kilovolts to hundreds of kilovolts, a large amount of secondary ions are emitted from the work surface. If the work surface partially has an insulated portion, positive electric charges are rapidly accumulated at the surface of the insulated portion due to the positive ions, which are implanted into the other portion, i.e., the conductive portion and the end of the insulated portion, and emitted secondary electrons. As a result, an electric field formed by the positive charges causes irregularities in the ion implantation distribution at the conductive portion, and discharge occurs between the surface of the insulated portion and the surface of the conductive portion supplied with the negative high-voltage pulse so that the surface of these portions may be destroyed.